The invention relates to a semiconductor device of the planar kind comprising a substrate made of a semiconductor material having a first kind of conductivity, in which a region having a second type of conductivity is formed and constitutes a PN junction with the first-type region. The invention also relates to a method of constructing such a device. More particularly, the invention relates to a device of the kind in question intended inter alia for forming a photovoltaic detector, in which the substrate is made of an alloy of two materials, having different forbidden band widths (or forbidden energy gaps), the width of the forbidden band of the alloy being dependent on the relative proportions of the two materials in the alloy, the two materials preferably being cadmium telluride and mercury telluride. Finally, the invention relates to a method of constructing a photovoltaic detector in which the substrate is a semiconductor material having the formula Cd.sub.x Hg.sub.1-x Te, x being a non-zero number less than 1.
Photovoltaic detectors comprising a substrate based on an alloy having the formula Cd.sub.x Hg.sub.1-x Te are of use inter alia in detecting infrared radiation. They are generally made from a P type substrate into the surface of which an impurity such as mercury is diffused, so as to produce a type N surface region of the substrate and thus form a PN junction. The sensitive surface of a detector of this kind is the surface of the substrate into which the impurity has been diffused. A method of constructing such a detector is described e.g. in French Pat. No. 1,504,497 filed on May 27, 1966 by the CNRS.
In most applications of photovoltaic detectors, more particularly in the infrared, it is important for the sensitivity to be high. French Patent Application No. 74 27 282 filed on Aug. 6, 1974 describes a method for improving the sensitivity of such detectors.
The method has been used to obtain a detector of the aforementioned kind comprising an adaptation layer whereby the electric and mechanical characteristics of the photovoltaic detector can be improved.
An object of the invention is to provide a photovoltaic detector having even greater sensitivity to radiation.
Another object of the invention is to construct the detector in a simple, economic manner.